And it ended a miserable week for the Frenchman, who saw his side falter in three competitions.

Wenger watched his team labour to an FA Cup draw against Championship side Hull, then put themselves on the brink of a Champions League exit at the hands of Barcelona.

"This is a fight where you keep going even when disappointment is there. Let's show we are prepared for the fight," he said.

Former Arsenal defender Lee Dixon's half-time tweet illustrated how important he felt victory would be for the Gunners' title challenge

Rashford makes his Marc again...

Barely anyone outside Old Trafford had heard of Marcus Rashford less than week ago - now the teenage United striker is a household name across the country.

Two goals on his senior debut in the Europa League against Midtjylland catapulted him into the national spotlight.

But, many asked, how would he fare against a league title-chasing side in the heat of a battle between two fierce rivals? Coolly, calmly and clinically, as it turned out.

Rashford only had two touches inside the Arsenal box inside the opening 35 minutes - but that is all he needed...

Rashford showed signs of his youthful exuberance in the early stages, darting inside a pair of Arsenal defenders from the left touchline before being hauled down on the edge of the penalty area.

The opportunity of that set-piece was not taken by the Red Devils, but it mattered little as Rashford soon put them into a two-goal lead.

The young Mancunian pounced on a poor clearance by Arsenal centre-back Gabriel to slot in his first Premier League goal, then waltzed into space to powerfully head in Jesse Lingard's floated cross.

But it was not just his finishing that caught the eye. Rashford showed great awareness and composure to pick out the run of Herrera, whose 20-yard shot took a wicked deflection off Arsenal defender Laurent Koscielny.

No wonder he was given a standing ovation from the Old Trafford crowd when he was replaced in the 80th minute.

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Marcus Rashford a special talent - Van Gaal

Former England winger Trevor Sinclair on BBC Radio 5 live:

"It's not just about the goals with Marcus Rashford. He has a cultured touch, his awareness is great and his link play is very good.

Something else impressed me too; the way he went to close down Petr Cech when the Arsenal goalkeeper received a back pass.

"Most young players would just close down the keeper, but Rashford shut off the pass out as well, and Cech ended up giving away the ball. That tells me he has been coached properly."

Van Gaal takes a tumble

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Man Utd boss Louis van Gaal takes a bizarre tumble

Manchester United manager Louis van Gaal fell over in front of the fourth official in what was described as "the comedy moment of the season" by BBC Radio 5 live commentator Conor McNamara.

The Dutchman, who rarely leaves his seat in the dugout during matches, appeared to be frustrated by an alleged dive by Gunners striker Alexis Sanchez.

"I have had a lot of criticism because I am sitting on my bench and now I am off my bench and I have lot of criticism because I'm doing that," Van Gaal said.

Grim up north for the Gunners...

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Arsenal must come back stronger - Wenger

Arsenal have not enjoyed their Premier League visits to Old Trafford in recent seasons, failing to pick up three points there since September 2006.

And many felt the Gunners needed to finally win at Old Trafford if they are going to end an even longer barren run - becoming the English champions.

The opportunity to beat United was probably the easiest for Arsenal than any other time during Arsene Wenger's 20-year reign.

But their defensive errors cost them dearly.

"I cannot fault the commitment and desire but unfortunately we conceded two easy goals," said Wenger afterwards.

Man of the match - Marcus Rashford

There's only one option - Manchester United striker Rashford. Two goals, one assist and another exciting all-round display from the teenage newcomer

Stats of the day

Rashford, aged 18 years and 120 days, is exactly the same age as Wayne Rooney was on the day that they both scored their first Premier League brace

Rashford is one of only six players to have had a hand in three goals on their Premier League debut

Arsenal have won none and lost seven of their past nine league trips to Old Trafford

Mesut Ozil assisted for the 18th occasion this season in the league - only Thierry Henry (20 in 2002-03) has more in a single campaign

Ozil scored and assisted in the same league away game for only the second time

Arsenal have only won two of their past eight league away matches (W2 D3 L3) - this following a run of 12 away matches where they won 10

Manchester United have now won back-to-back Premier League home games for the first time since September

What's next?

A couple of days rest and then straight back into Premier League action. The top flight reconvenes for a full midweek programme, with both teams facing home matches on Wednesday.

Arsenal look to bounce back against 16th-placed Swansea, while United welcome 10th-placed Watford.